Hydrogen occluding alloy

Abstract

The present invention provides a hydrogen occluding alloy exhibiting high hydrogen absorption and desorption rates, and excellent initial activation in practical use, and a method of making it. There is provided a hydrogen occluding alloy having a composition comprising, by wt %, 32 to 38% of rare earth elements essentially consisting of La and/or Ce, 0.5 to 3.5% of Al, 0.5 to 10% of Mn, 0.005 to 0.5% of hydrogen, optionally 0.1 to 17% of Co, and the balance being Ni and unavoidable impurities; wherein the alloy has a microstructure characterized in that fine rare earth element hydride is dispersively distributed in a matrix having a CaCu 5 -type crystal structure in a ratio of 0.5 to 20% by area. There are also provided electrodes and batteries containing such alloys, and methods of making and using such electrodes and batteries.

We claim: 
     
       1. A hydrogen occluding alloy having a composition comprising, by wt %, 32 to 38 of rare earth element,   0.5 to 3.5% of Al,   0.5 to 10% of Mn,   0.005 to 0.5% of hydrogen, and   the balance being Ni and unavoidable impurities;   said alloy having a microstructure comprising fine rare earth element hydride dispersively distributed in a matrix having a CaCu 5  -type crystal structure in a ratio of 0.5 to 20% by area.   
     
     
       2. A hydrogen occluding alloy as recited in claim 1, wherein said rare earth element comprises La and/or Ce. 
     
     
       3. An electrode for a Ni-hydrogen battery, said electrode comprising an alloy as recited in claim 1. 
     
     
       4. A hydrogen occluding alloy having a composition comprising, by wt %, 32 to 38 of rare earth element,   0.1 to 17% of Co,   0.5 to 3.5% of Al,   0.5 to 10% of Mn,   0.005 to 0.5% of hydrogen, and   the balance being Ni and unavoidable impurities;   said alloy having a microstructure comprising fine rare earth element hydride dispersively distributed in a matrix having a CaCu 5  -type crystal structure in a ratio of 0.5 to 20% by area.   
     
     
       5. A hydrogen occluding alloy as recited in claim 4, wherein said rare earth element comprises La and/or Ce. 
     
     
       6. An electrode for a Ni-hydrogen battery, said electrode comprising an alloy as recited in claim 4. 
     
     
       7. A hydrogen occluding alloy having a composition comprising, by wt %, 32 to 35 of rare earth element,   0.5 to 3.5% of Al,   0.5 to 10% of Mn,   0.005 to 0.2% of hydrogen, and   the balance being Ni and unavoidable impurities;   said alloy having a microstructure comprising fine rare earth element hydride dispersively distributed in a matrix having a CaCu 5  -type crystal structure in a ratio of 0.5 to 10% by area.   
     
     
       8. A hydrogen occluding alloy as recited in claim 7, wherein said rare earth element comprises La and/or Ce. 
     
     
       9. An electrode for a Ni-hydrogen battery, said electrode comprising an alloy as recited in claim 7. 
     
     
       10. A hydrogen occluding alloy having a composition comprising, by wt %, 32 to 35 of rare earth element,   4 to 17% of Co,   0.5 to 3.5% of Al,   0.5 to 10% of Mn,   0.005 to 0.2% of hydrogen, and   the balance being Ni and unavoidable impurities;   said alloy having a microstructure comprising fine rare earth element hydride dispersively distributed in a matrix having a CaCu 5  -type crystal structure in a ratio of 0.5 to 10% by area.   
     
     
       11. A hydrogen occluding alloy as recited in claim 10, wherein said rare earth element comprises La and/or Ce. 
     
     
       12. An electrode for a Ni-hydrogen battery, said electrode comprising an alloy as recited in claim 10. 
     
     
       13. A hydrogen occluding alloy formed according to a process comprising: (a) preparing an alloy ingot having a composition comprising, by weight:   32 to 38 of rare earth element,   0.5 to 3.5% of Al,   0.5 to 10% of Mn,   0.005 to 0.5% of hydrogen, and   the balance being Ni and unavoidable impurities;   (b) then subjecting said alloy to a hydrogen atmosphere of a pressure in the range of from 1 to 2 atms at a temperature of from about 0 to 100° C.;   (c) then heating the alloy to a temperature in the range of from 600 to 950° C.;   (d) and then cooling the alloy.   
     
     
       14. A hydrogen occluding alloy as recited in claim 13, wherein said process further comprises temper-annealing said alloy by heating said alloy ingot to a temperature of from about 850 to 1050° C. before said subjecting said alloy to a hydrogen atmosphere of a pressure in the range of from 1 to 2 atms at a temperature of from about 0 to 100° C.